The long term goal of my laboratory program is to apply the "one- bead one-compound" combinatorial library method (that was originally developed in my laboratory) to basic research and drug discovery involving the areas of infectious disease and cancer. Development and spread of multi-resistant bacterial pathogens are becoming one of the major problems in clinical Medicine. From 1/1/89 to 3/31/93, 16,571 cases of enterococci noscomial infections in hospitals were reported to the National Noscomial Infection Surveillance system. It was alarming to notice that during this 4 year period, enterococcal isolates resistant to vancomycin, particularly from patients in intensive care units, rose from 0.3% to 13.0% and the rate continued to rise in 1994 and 1995. There is a definite need for the development of new antibiotics that are effective in the treatment of vancomycin-resistant infections. Vancomycin works by binding tightly to peptidoglycan strands in the bacterial cell wall terminates in D-Ala-D-Ala. This complexation blocks transglycosylation and transpeptidation of nascent peptidoglycan strands. As a result, the peptidoglycan structure is weakened rendering the bacteria susceptible to osmotic lysis. Vancomycin resistant cells have replaced the normal D-Ala- D-Ala peptidoglycan termini with D-Ala-D-Lactate termini that are no longer recognized by vancomycin. In this proposal we hypothesize that using D-Ala-D-Ala as a probe to screen "one-bead one-compound" combinatorial peptide libraries, we will be able to identify D-Ala-D-Ala binders that have antibacterial activity. We further hypothesize that an antibiotic that can overcome vancomycin resistance can be discovered by screening combinatorial libraries with a D-Alan-D-Lactate probe. Tow assay approaches will be used for the library screening: the enzyme-linked colorimetric assay and the radiometric assay. The positive leads will be resynthesized and their antibacterial activity as well as physico-chemical interaction with D-Ala-D-Lactate will be determined. The active leads will then be further optimized with various approaches. Peptide libraries with secondary or constrained structures will be used in this study.